1. Field of the Invention
The present invention generally relates to signal distribution systems such as cable access television (CATV) systems and, more particularly, to cable customer drop condition monitoring and upstream communications for condition reporting.
2. Description of the Prior Art
Cable access television (CATV) is in widespread use and large systems for distributing large numbers of channels of programming from a central facility to large numbers of subscribers have been installed in at least most metropolitan areas of the United States. At present, there is substantial interest in using the cable facilities for additional purposes that may involve transmission from subscribers to the central facility such as Internet access, home shopping, interactive programming and the like in view of the large band width available thereon. Numerous arrangements have been proposed to provide or adapt CATV systems to permit bi-directional signalling over the cable facilities. Communications from subscribers to a central facility or subdivisions thereof has become generally referred to as “upstream” communications.
Such proposals have generally been characterized by complexity and large expense of the subscriber hardware which may or may not be justified by the subscriber's needs. Certainly, the subscriber hardware necessary for upstream communications is beyond that which is economically feasible to include as a standard feature of subscriber installations at the present time since CATV systems may service several hundred thousand subscribers, and particularly because only a small fraction of subscribers may wish to have upstream communication capability in an original installation. The provision for upstream communications in a device additional to the standard set-top box (STB) is also inconvenient and unsightly and significant customer resistance to such an arrangement is anticipated.
At a much more basic level, however, CATV systems have substantially become utilities for service to a large fraction of the public. Accordingly, it is desirable to monitor the condition of subscriber hardware, sometimes referred to as a cable drop or terminal unit. If the cable drop cannot be kept in service, a refund of a portion of subscriber fees may be required to reflect the loss of service to the subscriber. In such a case, it is important for the CATV system operator to be able to document substantially exact periods during which service was not provided.
Such information, including frequency of loss of functionality is also important to scheduling of maintenance and, perhaps more importantly, to relationships with subscribers. Of course, reliability of any monitoring system is of paramount importance and large operating margins are very desirable but have generally implied a trade-off with the signal distribution system capacity to provide other upstream communications that may be desired as well as acceptably high frequency of polling of each individual cable drop. By the same token, provision for maintaining the monitoring system itself is desirable and the reduction or interruption of monitoring capacity during such maintenance may compromise the monitoring function.
While the amount of information derived from condition monitoring of cable drops may be relatively less than might be required for other types of upstream communications over the CATV system, more or less continuous monitoring of cable drop condition implies a need for substantially continuous and simultaneous upstream communications from all (e.g. up to one hundred thousand) subscribers over a communication link. Functionally simultaneous communications from such a potentially large number of subscribers presents difficulty in identifying specific communications from individual subscribers or cable drops.
For example, frequency multiplexing requires wide bandwidth since the frequencies used must be well-separated and cannot be harmonically related. Time multiplexing requires a large number of time slots which must each be substantially larger than transmission delay over the system to avoid ambiguity. Coded communications requires decoders of substantial complexity and an increased amount of data (to identify the subscriber), both communicated and stored, as well as some synchronization of transmissions. All of these and other techniques proposed to date also present difficulties in integration with or retrofitting to existing systems.
Further, any upstream communication facility requires transmission circuits to be effectively provided in each cable drop and the expense cannot generally be passed along to the subscriber. Moreover, such monitoring must not interfere with the capacity of the CATV system to provide other services that involve upstream communications that particular subscribers may desire and which are likely to be in much greater demand in the near future. At the current state of the art, there has been no proposal which can simultaneously satisfy these communications requirements for even rudimentary monitoring of cable drop condition, particularly in regard to the prohibitive cost of providing such facilities individually for large numbers of cable drops.
If such monitoring could be provided, however, valuable services could be rendered to the customers and to the public at large. For example, subscriber sets for CATV systems obtain power from electrical utilities and power outage could be resolved to individual residences through the CATV system. (The CATV provider also has an interest in maintaining service to its subscribers and, further, the CATV system may be a source of emergency information to the public which must be maintained in the interest of the public safety.) Additionally, knowledge of the availability of power to CATV systems is a necessary incident of remote diagnostics of the cable drop condition, regardless of what other operational conditions may or may not be monitored. While the above problems are particularly evident in regard to CATV systems at the present time, it is evident that the nature of other signal distribution or communication systems may present similar difficulties in remote monitoring of the condition of individual subscriber equipment.